Legacy Document

Inside Macintosh: Mac OS Runtime Architectures /

Chapter 10 - Classic 68K Runtime Architecture / Bypassing MC68000 Addressing Limitations

Increasing the Size of the Jump Table

To increase the size of the jump table, use the -wrap option of the ILink command. This increases the memory allocated for the jump table at the expense of memory reserved for global data. In effect, this puts some of the jump table at negative offsets from A5.

This method is particularly useful for MacApp programs because they make little demand on global data space. However, at best, this method can only double the jump table size.

If you choose this option, intersegment calls, which are always routed through the jump table, might look like global references, as in this example:

JSR -48(A5)

The instruction used, JSR or BSR, makes it plain that it is not a global variable that is being referenced.